Alkaline dry batteries

ABSTRACT

An alkaline dry battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an alkaline electrolytic solution contained in the positive electrode, the negative electrode and the separator. The negative electrode includes a negative electrode active material including zinc, and an additive. The additive includes at least one selected from the group consisting of maleic acid, maleic anhydride and maleate salts.

TECHNICAL FIELD

The present invention relates to an improvement of a negative electrodein an alkaline dry battery.

BACKGROUND ART

Alkaline dry batteries (alkaline manganese dry batteries) have a largercapacity and can draw a larger current than manganese dry batteries, andthus have found widespread use. An alkaline dry battery includes apositive electrode, a negative electrode, a separator disposed betweenthe positive electrode and the negative electrode, and an alkalineelectrolytic solution contained in the positive electrode, the negativeelectrode and the separator. The negative electrode contains a negativeelectrode active material including zinc.

When a plurality of alkaline dry batteries are used in a device by beingconnected in series, one of the alkaline dry batteries may beerroneously reversed and charged. In other cases, primary alkaline drybatteries may be accidentally charged on secondary battery chargers.

If an alkaline dry battery is charged by misuse, hydrogen is generatedinside the battery to raise the internal pressure of the battery. Whenthe internal pressure of the battery reaches a predetermined value as aresult of the generation of a large amount of hydrogen, a safety valveis actuated to release hydrogen from the inside of the battery to theoutside. During this process, an alkaline electrolytic solution may leakto the outside along with the release of hydrogen to the outside, andthe alkaline electrolytic solution that has leaked may damage thedevice.

To prevent an alkaline electrolytic solution from leaking to the outsidein the event of erroneous charging of an alkaline dry battery, PatentLiterature 1 proposes to add zinc oxide to the alkaline electrolyticsolution.

CITATION LIST Patent Literature

PTL 1: Japanese Published Unexamined Patent Application No. 2006-156158

SUMMARY OF INVENTION

As erroneous charging of an alkaline dry battery continues, zincdeposition occurs in the negative electrode by the reduction of zincions in the electrolytic solution, resulting in a decrease in the amountof zinc ions in the electrolytic solution. With less zinc ions in theelectrolytic solution, the resistance on the zinc deposition reactionincreases significantly and the negative electrode potential lowerssharply, with the result that a hydrogen generation potential is reachedearly. As a result, hydrogen is generated in a large amount and a safetyvalve is actuated to release hydrogen to the outside together with thealkaline electrolytic solution leaking to the outside.

An aspect of the present disclosure resides in an alkaline dry batterywhich includes a positive electrode, a negative electrode, a separatordisposed between the positive electrode and the negative electrode, andan alkaline electrolytic solution contained in the positive electrode,the negative electrode and the separator, wherein the negative electrodeincludes a negative electrode active material including zinc, and anadditive, and the additive includes at least one selected from the groupconsisting of maleic acid, maleic anhydride and maleate salts.

The alkaline dry battery according to the present disclosure can preventa leakage of the alkaline electrolytic solution to the outside of thebattery even when charged erroneously.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a partially sectional front view of an alkaline dry battery inan embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

An alkaline dry battery according to an embodiment of the presentinvention includes a positive electrode, a negative electrode, aseparator disposed between the positive electrode and the negativeelectrode, and an alkaline electrolytic solution (hereinafter, simplywritten as the electrolytic solution) contained in the positiveelectrode, the negative electrode and the separator. The negativeelectrode includes a negative electrode active material including zinc,and an additive. The additive includes at least one selected from thegroup consisting of maleic acid, maleic anhydride and maleate salts.

If an alkaline dry battery is charged by misuse, a reaction occurs inthe negative electrode in which zinc ions (Zn²⁺) contained in theelectrolytic solution are reduced and zinc deposits on the surface ofthe negative electrode active material. Consequently, the negativeelectrode potential is maintained around −1.4 V (vs. Hg/HgO) that is thereduction potential of zinc ions. If the charging of the alkaline drybattery continues further, zinc ions in the electrolytic solutiondecrease in number and the resistance on the above zinc depositionreaction increases, with the result that the negative electrodepotential falls below −1.7 V (vs. Hg/HaO) that is the decompositionpotential of water in the electrolytic solution (the hydrogen generationpotential). The zinc ions in the electrolytic solution are present aszinc complex ions: Zn(OH)₄ ²⁻.

When, in contrast, the additive described above is added to the negativeelectrode, the zinc deposition reaction is promoted even when the amountof zinc ions in the electrolytic solution is small, and the negativeelectrode potential can be retarded from reaching the hydrogengeneration potential. Consequently, even if the alkaline dry battery ischarged by misuse, the generation of hydrogen inside the battery and theleakage of the electrolytic solution to the outside of the battery aresuppressed.

It is probable that when the negative electrode potential is lowered dueto charging, the additive is reductively decomposed on the surface ofthe negative electrode active material to form a film (SEI: solidelectrolyte interface) on the surface of the negative electrode activematerial. Although the mechanism by which the additive contained in thenegative electrode promotes the zinc deposition reaction is unclear, theabove film will be one of the factors that affect the zinc depositionreaction on the surface of the negative electrode active material.

The zinc ions contained in the electrolytic solution include, forexample, part of zinc in the negative electrode active material which isdissolved in the electrolytic solution. The amount of zinc ionscontained in the electrolytic solution may be increased by adding zincoxide to the electrolytic solution. The concentration of zinc oxide inthe electrolytic solution is, for example, 1 to 5 mass %.

The additive includes at least one selected from the group consisting ofmaleic acid, maleic anhydride and maleate salts. Maleic acid and saltsthereof may be partially ionized and present as anions. Maleic anhydridemay be partially present as maleic acid by being hydrolyzed with waterin the electrolytic solution. Examples of the maleate salts includealkali metal salts, alkaline earth metal salts, onium salts and ammoniumsalts of maleic acid. Examples of the alkali metal salts include sodiumsalt and potassium salt. Examples of the alkaline earth metal saltsinclude magnesium salt and calcium salt.

To suppress the generation of hydrogen during erroneous charging of thealkaline dry battery, the additive preferably includes maleic anhydride.

The amount of the additive contained in the negative electrode ispreferably not less than 0.2 parts by mass and not more than 4 parts bymass per 100 parts by mass of the electrolytic solution contained in thenegative electrode. When the amount of the additive contained in thenegative electrode is 0.2 parts by mass or more per 100 parts by mass ofthe electrolytic solution contained in the negative electrode, theadditive offers sufficient effects in suppressing the hydrogengeneration. When the amount of the additive contained in the negativeelectrode is 4 parts by mass or less per 100 parts by mass of theelectrolytic solution contained in the negative electrode, a sufficientpacking density of the negative electrode active material is ensured.The amount of the additive contained in the negative electrode is morepreferably not less than 1 part by mass and not more than 2 parts bymass per 100 parts by mass of the electrolytic solution contained in thenegative electrode.

The positive electrode may contain the additive described above. Most ofthe additive added to the negative electrode remains in the negativeelectrode, but a very small proportion of the additive contained in theelectrolytic solution in the negative electrode may migrate to theelectrolytic solution in the positive electrode.

For purposes such as to control the viscosity, the negative electrodemay further contain a surfactant or an aromatic compound. Examples ofthe surfactants include polyoxyalkylene group-containing compounds andphosphoric acid esters, with phosphoric acid esters and alkali metalsalts thereof being preferable. A preferred aromatic compound isterephthalic acid.

Examples of the alkaline dry batteries according to an embodiment of thepresent invention include cylindrical batteries and coin batteries.

Hereinbelow, an alkaline dry battery according to an embodiment will bedescribed in detail with reference to the drawing. The present inventionis not limited to the embodiment described below. Further, the presentinvention may be modified appropriately without impairing theadvantageous effects of the present invention. Furthermore, theembodiment described below may be combined with other embodiments.

FIG. 1 is a half sectional front view of an alkaline dry batteryaccording to an embodiment of the present invention. FIG. 1 illustratesan example of cylindrical batteries having an inside-out structure. Asillustrated in FIG. 1, the alkaline dry battery includes a hollowcylindrical positive electrode 2, a gelled negative electrode 3 disposedin the hollow portion of the positive electrode 2, a separator 4arranged therebetween, and an electrolytic solution (not shown), andthese are accommodated in a bottomed cylindrical battery case 1 thatalso serves as a positive electrode terminal. The electrolytic solutionis an alkaline aqueous solution.

The positive electrode 2 arranged in contact with the inner wall of thebattery case 1. The positive electrode 2 contains manganese dioxide andthe electrolytic solution. The hollow portion of the positive electrode2 is filled with the gelled negative electrode 3 via the separator 4.The negative electrode 3 contains a negative electrode active materialincluding zinc, and the above additive, and usually further contains theelectrolytic solution and a gelling agent.

The separator 4 has a bottomed cylindrical shape and contains theelectrolytic solution. The separator 4 is composed of a cylindricalseparator 4 a and a bottom paper 4 b. The separator 4 a is arrangedalong the inner surface of the hollow portion of the positive electrode2 and separates the positive electrode 2 and the negative electrode 3from each other. Thus, the separator arranged between the positiveelectrode and the negative electrode means this cylindrical separator 4a. The bottom paper 4 b is arranged at the bottom of the hollow portionof the positive electrode 2 and separates the negative electrode 3 andthe battery case 1 from each other.

The opening of the battery case 1 is sealed with a sealing unit 9. Thesealing unit 9 is composed of a gasket 3, a negative electrode terminalplate 7 also serving as a negative electrode terminal, and a negativeelectrode current collector 6. The negative electrode current collector6 is inserted in the negative electrode 3. The negative electrodecurrent collector 6 has a nail-like shape having a head and a body. Thebody of the negative electrode current collector 6 is inserted in athrough hole provided in a central tubular portion of the gasket 5, andthe head is welded to a central flat portion of the negative electrodeterminal plate 7. The open end of the battery case 1 is crimped to aflange portion of the peripheral edge of the negative electrode terminalplate 7 via an outer peripheral end portion of the gasket 5. An exteriorlabel 8 is attached to cover the exterior surface of the battery case 1.

The alkaline dry battery will be described in detail below.

(Negative Electrodes)

Examples of the negative electrode active materials include zinc andzinc alloys. From the point of view of corrosion resistance, the zincalloy may include at least one selected from the group consisting ofindium, bismuth and aluminum. The indium content in the zinc alloy is,for example, 0.01 to 0.1 mass %, and the bismuth content is, forexample, 0.003 to 0.02 mass %. The aluminum content in the zinc alloyis, for example, 0.001 to 0.03 mass %. From the point of view ofcorrosion resistance, the proportion of elements other than zinc in thezinc alloy is preferably 0.025 to 0.08 mass %.

The negative electrode active material is usually used in the form of apowder. From the points of view of the packing density of the negativeelectrode and the diffusibility of the electrolytic solution within thenegative electrode, the average particle size (D50) of the negativeelectrode active material powder is, for example, 100 to 200 μm, andpreferably 110 to 160 μm. Incidentally, the average particle size (D50)in the present specification is the median diameter in a volume-basedgrain size distribution. The average particle size is determined using,for example, a laser diffraction/scattering particle size distributionanalyzer.

For example, the negative electrode is obtained by mixing particles ofthe zinc-containing negative electrode active material, the additivedescribed above, a gelling agent, and an electrolytic solution.

The gelling agent is not particularly limited and may be any knowngelling agent used in the field of alkaline dry batteries. For example,a water-absorbing polymer or the like may be used. Examples of suchgelling agents include polyacrylic acid and sodium polyacrylate.

The gelling agent is added in an amount of, for example, 0.5 to 2.5parts by mass per 100 parts by mass of the negative electrode activematerial.

For purposes such as to control the viscosity, a surfactant or anaromatic compound may be added to the negative electrode. Thesurfactants and the aromatic compounds used here may be those describedhereinabove. To ensure that the surfactant and the aromatic compoundwill be dispersed in the negative electrode more uniformly, it ispreferable that the surfactant and the aromatic compound be addedbeforehand to the electrolytic solution used in the fabrication of thenegative electrode.

A compound which contains a metal with a high hydrogen overvoltage suchas indium or bismuth may be appropriately added to the negativeelectrode in order to enhance the corrosion resistance. To suppress thegrowth of dendrites such as zinc oxide, a small amount of a silicic acidcompound such as a silicic acid or a potassium salt thereof may beappropriately added to the negative electrode.

(Negative Electrode Current Collectors)

Examples of the materials of the negative electrode current collectorthat is inserted in the gelled negative electrode include metals andalloys. The negative electrode current collector preferably includescopper, and may be made of, for example, an alloy containing copper andzinc such as brass. Where necessary, the negative electrode currentcollector may be plated with tin or the like.

(Positive Electrodes)

The positive electrode usually contains manganese dioxide as thepositive electrode active material, and further a conductive agent andan electrolytic solution. Where necessary, the positive electrode mayfurther contain a binder.

The manganese dioxide is preferably electrolytic manganese dioxide.Examples of the crystal structures of the manganese dioxide includeα-type, β-type, γ-type, δ-type, ε-type, η-type, λ-type and ramsdellitetype.

The manganese dioxide is used in a powder form. To easily ensureproperties such as the packing density of the positive electrode and thediffusibility of the electrolytic solution within the positiveelectrode, the average particle size (D50) of the manganese dioxide is,for example, 25 to 60 μm.

From the points of view of formability and the suppression of positiveelectrode expansion, the BET specific surface area of the manganesedioxide may be in the range of, for example, 20 to 50 m²/g. The BETspecific surface area is determined by measuring and calculating thesurface area using the BET equation that is a theoretical equationdescribing multilayer molecular adsorption. The BET specific surfacearea may be determined by, for example, a nitrogen adsorption methodusing a specific surface area measuring device.

Examples of the conductive agents include carbon blacks such asacetylene black, and other conductive carbon materials such asgraphites. Some example graphites which may be used are naturalgraphites and artificial graphites. The conductive agent may be fibersor the like, and is preferably a powder. The average particle size (D50)of the conductive agent is, for example, 3 to 20 μm.

For example, the content of the conductive agent in the positiveelectrode is 3 to 10 parts by mass, and preferably 5 to 9 parts by massper 100 parts by mass of the manganese dioxide.

Silver and silver compounds such as Ag₂O, AgO, Ag₂O₃ and AgNiO₂ may beadded to the positive electrode to absorb hydrogen that is generatedinside the alkaline dry battery during erroneous charging of thebattery.

For example, the positive electrode is obtained by compacting into apellet a positive electrode mixture including a positive electrodeactive material, a conductive agent, an alkaline electrolytic solutionand optionally a binder. Alternatively, the positive electrode mixturemay be formed into flakes or granules, classified as required, andcompacted into a pellet.

The pellet, after placed into the battery case, may be secondarilypressed using a predetermined tool so as to be in close contact with theinner wall of the battery case.

(Separators)

Examples of the separator materials include celluloses and polyvinylalcohols. The separator may be a nonwoven fabric mainly composed offibers of the above material, or may be a microporous film such as ofcellophane or polyolefin. A nonwoven fabric and a microporous film maybe used in combination. Examples of the nonwoven fabrics includenonwoven fabrics made from a mixture based on cellulose fibers andpolyvinyl alcohol fibers, and nonwoven fabrics made from a mixture basedon rayon fibers and polyvinyl alcohol fibers.

In FIG. 1, the bottomed cylindrical separator 4 is composed of thecylindrical separator 4 a and the bottom paper 4 b. The bottomedcylindrical separator is not limited to this configuration, and aseparator with a known shape used in the field of alkaline dry batteriesmay be used. The separator may be composed of a single sheet, or theseparator may be composed of a plurality of thin sheets stacked on topof one another. The cylindrical separator may be formed by winding athin sheet multiple times.

For example, the thickness of the separator is 200 to 300 μm. Theseparator preferably has the above thickness as a whole. If a sheet forforming the separator is thin, a plurality of the sheets may be stackedto attain the thickness described above.

(Electrolytic Solutions)

The electrolytic solution is contained in the positive electrode, thenegative electrode and the separator. For example, the electrolyticsolution is an alkaline aqueous solution containing potassium hydroxide.The concentration of potassium hydroxide in the electrolytic solution ispreferably 30 to 50 mass %. The electrolytic solution may furthercontain zinc oxide. For example, the concentration of zinc oxide in theelectrolytic solution is 1 to 5 mass %.

(Gaskets)

Examples of the materials of the gaskets include polyamide, polyethyleneand polypropylene. For example, the gasket is obtained by injectionmolding the above material into a predetermined shape. From the point ofview of facilitating the permeation of hydrogen, preferred gasketmaterials are 6,10-nylon, 6,12-nylon and polypropylene. The gasketusually has an explosion-proof thin portion. In order to increase theamount of hydrogen permeation, the thin portion is preferably annular.The gasket 5 in FIG. 1 has an annular thin portion 5 a.

(Battery Cases)

For example, the battery case is a bottomed cylindrical metal case. Themetal case is, for example, a nickel-plated steel sheet. To attain goodadhesion between the positive electrode and the battery case, thebattery case that is used is preferably a metal case in which the innersurface is covered with a carbon coating.

EXAMPLES

The present invention will be described in detail hereinbelow based onEXAMPLES and COMPARATIVE EXAMPLES. However, it should be construed thatthe scope of the present invention is not limited to the EXAMPLESdescribed below.

Example 1

Cylindrical AA alkaline dry batteries (LR6) illustrated in FIG. 1 wereproduced in accordance with the following procedures (1) to (3).

(1) Fabrication of Positive Electrode

A graphite powder (average particle size (D50): 8 μm) as a conductiveagent was added to an electrolytic manganese dioxide powder (averageparticle size (D50): 35 μm) as a positive electrode active material togive a mixture. The mass ratio of the electrolytic manganese dioxidepowder to the graphite powder was 92.4:7.6. The electrolytic manganesedioxide powder used had a specific surface area of 41 m²/g. Anelectrolytic solution was added to the mixture, and the resultantmixture was sufficiently stirred and compacted into flakes. A positiveelectrode mixture was thus obtained. The mass ratio of the mixture tothe electrolytic solution was 100:1.5. The electrolytic solution usedwas an alkaline aqueous solution containing potassium hydroxide(concentration: 35 mass %) and zinc oxide (concentration: 2 mass %).

The flaky positive electrode mixture was crushed into granules, whichwere then classified through a 10-100 mesh sieve, and 11 g of thegranules thus obtained were compacted into predetermined hollowcylindrical shapes having an outer diameter of 13.65 mm. Two positiveelectrode pellets were thus produced.

(2) Fabrication of Negative Electrode

A gelled negative electrode 3 was obtained by mixing a zinc alloy powder(average particle size (D50): 130 μm) as a negative electrode activematerial, maleic anhydride as an additive, an electrolytic solution, agelling agent and terephthalic acid. The zinc alloy contained 0.02 mass% indium, 0.01 mass % bismuth and 0.005 mass % aluminum. Theelectrolytic solution used here was the same as the electrolyticsolution used in the fabrication of the positive electrode. The gellingagent used was a mixture of crosslinked branched polyacrylic acid andhighly crosslinked linear sodium polyacrylate. The amount of maleicanhydride added was 2 parts by mass per 100 parts by mass of theelectrolytic solution. The mass ratio of the negative electrode activematerial to the electrolytic solution and the gelling agent was100:50:1. The amount of terephthalic acid added was 0.15 parts by masswith respect to 99.85 parts by mass of the electrolytic solution.

(3) Assembling of Alkaline Dry Batteries

Varniphite manufactured by Nippon Kokuen Group was applied to the innersurface of a bottomed cylindrical battery case made of a nickel-platedsteel sheet (outer diameter: 13.80 mm, wall thickness of cylindricalportion: 0.15 mm, height: 50.3 mm) to form a carbon coating having athickness of about 10 μm. A battery case 1 was thus obtained. The twopositive electrode pellets were vertically inserted into the batterycase 1 and were then pressed to form a positive electrode 2 in closecontact with the inner wall of the battery case 1. A bottomedcylindrical separator 4 was arranged inside the positive electrode 2,and thereafter an electrolytic solution was poured to impregnate theseparator 4. The electrolytic solution used here was the same as theelectrolytic solution used in the fabrication of the positive electrode.The unit was then allowed to stand for a predetermined time to let theelectrolytic solution to permeate through the separator 4 into thepositive electrode 2. Thereafter, the inside of the separator 4 wasfilled with 6 g of the gelled negative electrode 3.

The separator 4 was composed of a cylindrical separator 4 a and a bottompaper 4 b. The cylindrical separator 4 a and the bottom paper 4 b werenonwoven fabric sheets (basis weight: 28 g/m²) made of a mixture basedon rayon fibers and polyvinyl alcohol fibers in a mass ratio of 1:1. Thenonwoven fabric sheet used as the bottom paper 4 b had a thickness of0.27 mm. The separator 4 a had been formed by winding a 0.09 mm thicknonwoven fabric sheet three times.

A negative electrode current collector 6 was obtained by pressinggeneral brass (Cu content: about 65 mass %, Zn content: about 35 mass %)into a nail shape, and plating the surface with tin. The diameter of thebody of the negative electrode current collector 6 was 1.15 mm. The headof the negative electrode current collector 6 was electrically welded toa negative electrode terminal plate 7 made of a nickel-plated steelsheet. Thereafter, the body of the negative electrode current collector6 was press-fitted into a central through hole in a gasket 5 mainlyformed of polyamide 6,12. In this manner, a sealing unit 9 was producedwhich was composed of the gasket 5, the negative electrode terminalplate 7 and the negative electrode current collector 6.

Next, the sealing unit 9 was installed at the opening of the batterycase 1. During this process, the body of the negative electrode currentcollector 6 was inserted into the negative electrode 3. The open end ofthe battery case 1 was crimped to the peripheral edge of the negativeelectrode terminal plate 7 via the gasket 5, thereby sealing the openingof the battery case 1. An exterior label 8 was applied to cover theexterior surface of the battery case 1. An alkaline dry battery A1 wasthus fabricated.

[Evaluation]

The batteries A1 fabricated as described above were evaluated by thefollowing test.

Four batteries A1 were provided. Three of the batteries were connectedin series, and the remaining one was connected to the three batterieswith its positive and negative terminals in the reversed direction. Anassembled battery was thus fabricated. A resistance of 7.5Ω wasconnected to the assembled battery, and the assembled battery wasallowed to stand for 15 minutes after the resistance was connectedthereto, in other words, the reversely connected battery was charged for15 minutes. Fifteen minutes after the resistance had been connected, thereversely connected battery was inspected for the presence or absence ofany leakage of the electrolytic solution.

The above evaluation test was performed 20 times. Of the twentyreversely connected batteries, the number of batteries which had leakedthe electrolytic solution was determined and the proportion thereof wascalculated as the leak occurrence rate.

The above evaluation test simulates a case where a battery iserroneously connected with its positive and negative terminals in thereversed direction from other batteries in a medium load device. Thecharging time of 15 minutes assumes that the user who has put thebatteries into the device will recognize an abnormal operation of thedevice and will notice the reversal of the battery and remove it in thisperiod of time.

Example 2

Alkaline dry batteries A2 were fabricated and evaluated in the samemanner as in EXAMPLE 1, except that maleic anhydride used as theadditive in the production of the negative electrode was replaced bymaleic acid.

Comparative Example 1

Alkaline dry batteries X1 were fabricated and evaluated in the samemanner as in EXAMPLE 1, except that no additive was used in theproduction of the negative electrode.

The evaluation results are described in Table 1

TABLE 1 Batteries Leak occurrence No. Additive rate (%) Comp. Ex. 1 X1None 50 Ex. 1 A1 Maleic anhydride 0 Ex. 2 A2 Maleic acid 10

The batteries A1 and A2 of EXAMPLES 1 and 2 in which the negativeelectrode contained the additive attained a lower leak occurrence ratethan the batteries X1 of COMPARATIVE EXAMPLE 1. In particular, thebatteries A1 of EXAMPLE 1 which involved maleic anhydride as theadditive achieved 0% leak occurrence rate.

Examples 3 to 6

Alkaline dry batteries A3 to A6 were fabricated and evaluated in thesame manner as in EXAMPLE 1, except that in the production of thenegative electrode, the amount of maleic anhydride added (per 100 partsby mass of the electrolytic solution used in the production of thenegative electrode) was changed as described in Table 2.

The evaluation results are described in Table 2.

TABLE 2 Batteries Amount of maleic anhydride Leak occurrence No. (partsby mass) rate (%) Ex. 3 A3 0.1 25 Ex. 4 A4 0.2 5 Ex. 5 A5 1 0 Ex. 1 A1 20 Ex. 6 A6 4 0

The batteries A3 to A6 of EXAMPLES 3 to 6 attained a lower leakoccurrence rate than the batteries X1 of COMPARATIVE EXAMPLE 1. Inparticular, a leak occurrence rate of 5% or less was achieved by thebatteries A1 and A4 to A6 of EXAMPLES 1 and 4 to 6 in which the amountof maleic anhydride contained in the negative electrode was 0.2 parts bymass to 4 parts by mass per 100 parts by mass of the electrolyticsolution contained in the negative electrode.

INDUSTRIAL APPLICABILITY

The dry batteries according to an embodiment of the present inventionmay be used in all kinds of devices that are powered by dry batteries.For example, the dry batteries are suited for such devices as portableaudio equipment, electronic games, lights and toys.

REFERENCE SIGNS LIST

-   -   1 BATTERY CASE    -   2 POSITIVE ELECTRODE    -   3 NEGATIVE ELECTRODE    -   4 BOTTOMED CYLINDRICAL SEPARATOR    -   4 a CYLINDRICAL SEPARATOR    -   4 b BOTTOM PAPER    -   5 GASKET    -   5 a THIN PORTION    -   6 NEGATIVE ELECTRODE CURRENT COLLECTOR    -   7 NEGATIVE ELECTRODE TERMINAL PLATE    -   8 EXTERIOR LABEL    -   9 SEALING UNIT

1. An alkaline dry battery comprising a positive electrode, a negativeelectrode, a separator disposed between the positive electrode and thenegative electrode, and an alkaline electrolytic solution contained inthe positive electrode, the negative electrode and the separator,wherein the negative electrode comprises a negative electrode activematerial comprising zinc, and an additive, and the additive comprises atleast one selected from the group consisting of maleic acid, maleicanhydride and maleate salts.
 2. The alkaline dry battery according toclaim 1, wherein the amount of the additive contained in the negativeelectrode is not less than 0.2 parts by mass and not more than 4 partsby mass per 100 parts by mass of the electrolytic solution contained inthe negative electrode.
 3. The alkaline dry battery according to claim1, wherein the additive comprises maleic anhydride.
 4. The alkaline drybattery according to claim 1, wherein the positive electrode comprisesthe additive.